Solid-state imaging device and method for manufacturing solid-state imaging device

ABSTRACT

A plurality of optical sensors ( 4 ) are arranged in a surface region of a semiconductor substrate ( 6 ) in a matrix pattern, and electric charge generated by the optical sensors ( 4 ) is transferred by first and second transfer electrodes ( 12  and  14 ) embedded under the optical sensors ( 4 ). The semiconductor substrate ( 6 ) is constructed by laminating a support substrate ( 16 ) composed of silicon, a buffer layer ( 18 ), and a thin silicon layer ( 20 ) composed of single-crystal silicon. p− regions ( 26 ) (overflow barrier) and n-type regions ( 28 ) which function as transfer paths are formed under the optical sensors ( 4 ). The first and the second transfer electrodes ( 12  and  14 ) are disposed between the buffer layer ( 18 ) and the n-type regions ( 28 ), and an insulating film ( 30 ) is interposed between the n-type regions ( 28 ) and the first and the second transfer electrodes ( 12  and  14 ). In this structure, the light-receiving area is large since the transfer electrodes are not disposed in the front region. Accordingly, the sensitivity can be ensured even when the size of the optical sensors ( 4 ) is reduced for increasing the number of pixels.

This application claims priority to Japanese Patent Application NumberJP2001-307349, filed Oct. 3, 2001 which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a solid-state imaging device.

BACKGROUND ART

Generally, solid-state imaging devices used in commercial digital stillcameras, which have recently become increasingly popular in the market,must have a million or more pixels in order to achieve an image qualityno less than that of a film camera, and those having three million ormore pixels have recently been put to practical use. Additionally, thecommercial digital still cameras are required to be reduced in size.Therefore, the number of pixels in the solid-state imaging devices mustbe increased without changing the chip size thereof, or the increase inthe number of pixels and reduction in the chip size must be achieved atthe same time.

Interline-transfer interlace-scan (IT-IS) CCDs are typically used assolid-state imaging devices with a large number of pixels. In this typeof solid-state imaging device, when the number of pixels is increasedwithout changing the chip size, the size of unit cells used forphotoelectric conversion reduces accordingly. Therefore, the sensitivityand the amount of charge which can be carried, that is, a saturationsignal level, are reduced. In order to compensate for this, variouscharacteristic improvements have been made so that the number of pixelscan be increased without causing the characteristic degradation due tothe reduction in the size of the unit cells. However, if the number ofpixels is further increased, the performance is inevitably degraded tosome extent.

In order to fundamentally solve the above-described problem, solid-stateimaging devices in which active devices, such as optical sensors andcharge transfer electrodes, are arranged in multiple layers have beenproposed, as described below.

(1) A method for increasing the sensitivity of a solid-state imagingdevice has been proposed in which a photoelectric conversion unitcomposed of polycrystal silicon or amorphous silicon is formed on asignal charge transfer unit so that the entire surface of thesolid-state imaging device functions as a light-receiving surface andthe amount of light received increases. However, since the mobility ofelectrons and holes in polycrystal silicon and amorphous silicon islower than that in single-crystal silicon, a problem of afterimage orthe like occurs. Accordingly, it is difficult to put this type ofsolid-state imaging device to practical use.

(2) A method has been proposed in which the thickness of a siliconsubstrate is reduced to about several tens of micrometers by backetching and an image is captured by causing light to enter opticalsensors from the back. In this method, the amount of incident lightincreases since it is not impeded by transfer electrodes, and thesensitivity increases accordingly. However, since there is a limit toreducing the thickness of the silicon substrate, the application islimited to cases where infrared light, for which silicon has hightransmittance, is received. In addition, it is difficult to increase theprecision, and therefore this structure is not suitable for imagingdevices with a large number of pixels which are required to be arrangedat high density.

(3) A frame transfer (FT) CCD in which a single unit functions as both aphotoelectric conversion unit and a charge transfer unit is alsoadvantageous in that it has a large effective-charge-storage area.However, there is a problem in that the sensitivity reduces in a shortwavelength region due to light absorption by transfer electrodes. Inaddition, the amount of dark current generated is large compared to anIT-CCD since a single unit functions as both the photoelectricconversion unit and the charge transfer unit, and there is a problem inthat the S/N ratio is low.

In order to solve the above-described problems, a main object of thepresent invention is to provide a solid-state imaging device having astructure such that the number of pixels can be increased withoutincreasing the size, and to provide a method for manufacturing thesolid-state imaging device.

DISCLOSURE OF INVENTION

In a solid-state imaging device according to the present invention and asolid-state imaging device manufactured by a method according to thepresent invention, electrodes are disposed between a buffer layer andoptical sensors, that is, behind the optical sensors. Accordingly, when,for example, the electrodes are used as charge transfer electrodes, itis not necessary to arrange the charge transfer electrodes on thelight-receiving surfaces of the optical sensors. In such a case, thelight-receiving area of the optical sensors can be increased compared tothe known structure.

In addition, when the electrodes are used as overflow drain electrodes,unnecessary charge stored in the optical sensors can be removed byapplying a voltage to the electrodes.

In addition, in the method for manufacturing the solid-state imagingdevice according to the present invention, an overflow barrier is formedby implanting ions into a silicon substrate through a first surface ofthe silicon substrate at low energy before the electrodes are formed onthe first surface of the silicon substrate, the overflow barrier beingpositioned under the optical sensors when the solid-state imaging deviceis completed. Accordingly, unlike the known structure, it is notnecessary to implant the ions deep into the silicon substrate to formthe overflow barrier. Therefore, the profile of the implanted impuritiescan be reliably controlled and the thickness of the overflow barrier canbe reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1, (A) and (B) are sectional side views of a part of asolid-state imaging device according to an embodiment of the presentinvention.

FIG. 2 is a plan view showing a part of the solid-state imaging deviceshown in FIG. 1.

FIG. 3 is a sectional side view of a part of a solid-state imagingdevice according to a second embodiment of the present invention.

FIG. 4 is a plan view showing a part of the solid-state imaging deviceaccording to the second embodiment.

FIGS. 5A, 5B, and 5C are process diagrams of an example of a method formanufacturing a solid-state imaging device according to the presentinvention.

FIGS. 6A, 6B, and 6C are process diagrams showing processes performedafter the process shown in FIG. 5C.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described below withreference to the accompanying drawings.

In FIG. 1, (A) and (B) are sectional side views of a part of asolid-state imaging device according to an embodiment of the presentinvention, and FIG. 2 is a plan view showing a part of the solid-stateimaging device shown in FIG. 1. FIG. 1(A) is a sectional view of FIG. 2cut along line A-A′, and FIG. 1(B) is a sectional view of FIG. 2 cutalong line B-B′.

As shown in FIG. 2, a solid-state imaging device 2 according to thepresent embodiment includes a plurality of optical sensors 4 arranged ina surface region of a semiconductor substrate 6 in a matrix pattern suchthat the optical sensors 4 are adjacent to one another. The opticalsensors 4 on each row are separated from one another bydevice-separating regions 8, as shown also in FIG. 1(B), and the opticalsensors 4 on each column are separated from one another by channel-stopregions 10, as shown also in FIG. 1 (A). The channel-stop regions 10 arep-type regions formed by implanting p-type impurity ions at highconcentration. FIG. 2 shows the structure under a light-shielding film,which will be described below.

Each optical sensor 4 is provided with first and second transferelectrodes 12 and 14 (electrodes according to the present invention) fortransferring signal charge generated by the optical sensor 4 when itreceives light. The first and the second transfer electrodes 12 and 14are provided in common for the optical sensors 4 on each row, and extendalong the rows of the optical sensors 4. In addition, the first and thesecond transfer electrodes 12 and 14 are arranged alternately along thecolumns of the optical sensors 4. As shown in FIG. 1, according to thepresent embodiment, the first and the second transfer electrodes 12 and14 are not provided on the surface of the semiconductor substrate 6 butare embedded under (behind) the optical sensors 4.

The semiconductor substrate 6 is constructed by laminating a supportsubstrate 16 composed of silicon, a buffer layer 18 composed of aninsulating material, and a thin silicon layer 20 (single-crystal siliconthin film), in that order from the bottom. The thin silicon layer 20 hasthe optical sensors 4 in a surface region thereof, and the opticalsensors 4 are composed of, for example, p+ regions 22 in which p-typeimpurities are implanted at high concentration and n-type regions 24 inwhich n-type impurities are implanted. In addition, p− regions 26 inwhich p-type impurities are implanted at low concentration are providedunder the optical sensors 4 as an overflow barrier, and n-type regions28 in which n-type impurities are implanted, for example, are providedunder the p− regions 26 as transfer paths for transferring the signalcharge generated by the optical sensors 4.

The first and the second transfer electrodes 12 and 14 are embeddedbetween the buffer layer 18 and the n-type regions 28, and an insulatingfilm 30 is interposed between the n-type regions 28 and the first andthe second transfer electrodes 12 and 14. The first and the secondtransfer electrodes 12 and 14 may be composed of, for example,polysilicon or a metal such as aluminum and tungsten, and the insulatingfilm 30 may be composed of, for example, silicon oxide, silicon nitride,titanium oxynitride, silicon carbide, etc. As shown in FIG. 1(A), thefirst and the second transfer electrodes 12 and 14 are separated fromeach other by an insulating layer. In the present embodiment, the firsttransfer electrodes 12 are positioned directly under the optical sensors4, and the second transfer electrodes 14 are positioned under thechannel-stop regions 10.

An antireflection film 32 is formed on the surfaces of the opticalsensors 4 to prevent the reflection of light entering the opticalsensors 4, so that the amount of light entering the optical sensors 4increases. The antireflection film 32 may be composed of silicon oxideor silicon nitride. A light-shielding film 34 having apertures atpositions corresponding to the optical sensors 4 is formed on the thinsilicon layer 20 with an insulating layer provided therebetween. Inaddition, a planarizing film 38 is formed on the light-shielding film34, and a color filter 40 and an on-chip lens 42 are formed similarly tothose in the known solid-state imaging device.

Next, the operation of the solid-state imaging device 2 constructed asabove will be described below.

When an image is captured, a mechanical shutter (not shown) placed infront of the solid-state imaging device 2 is released so that lightenters each of the optical sensors 4. Each optical sensor 4 performsphotoelectric conversion of the light to generate signal charge, andaccumulates the generated signal charge. Then, when the mechanicalshutter is closed and the exposure is finished, transfer pulses aresuccessively applied to the first and the second transfer electrodes 12and 14, and unnecessary charge stored in the transfer paths during theexposure is removed.

Next, a positive voltage is applied to alternate first transferelectrodes 12, for example, to N^(th) first transfer electrodes 12 whereN is an even number, so that the signal charge accumulated in thecorresponding optical sensors 4 is read out and supplied to the n-typeregions 28, which function as the transfer paths. In this embodiment,the signal charge is read out by the interlace method, and therefore apositive voltage is applied to the alternate first transfer electrodes12 as above.

Then, transfer pulses are applied to the first and the second transferelectrodes 12 and 14, so that the signal charge read out as above issuccessively transferred toward horizontal charge transfer registers(not shown) along the direction in which the first and the secondtransfer electrodes 12 and 14 are arranged. Thus, the signal chargegenerated by the optical sensors 4 on each row is supplied to thecorresponding horizontal charge transfer register. Then, the signalcharge is transferred by the horizontal charge transfer registers,converted into a voltage, and output from the solid-state imaging device2 as an image signal.

Then, a positive voltage is applied to M^(th) first transfer electrodes12 where M is an odd number so that the signal charge is read out fromthe corresponding optical sensors 4. Then, similar to the above,transfer pulses are applied to the first and the second transferelectrodes 12 and 14 so that the signal charge is successivelytransferred. Accordingly, the signal charge generated by all of theoptical sensors is read out from the optical sensors 4, and an imagesignal representing the captured image is output from the solid-stateimaging device 2.

In the solid-state imaging device 2 according to the present embodiment,the transfer electrodes are not formed on the surface of the thinsilicon layer 20 as in the known structure, and therefore the area ofthe optical sensors 4 is increased compared to the known structure.Accordingly, a sufficient amount of light enters the optical sensors 4.Therefore, even when the size of each unit cell (pixel) is reduced toincrease the number of pixels without increasing the size of thesolid-state imaging device 2, required sensitivity can be achieved andthe number of pixels in the solid-state imaging device 2 can be furtherincreased.

In addition, in the case in which the size of each unit cell is the sameas that in the known structure, the sensitivity of the solid-stateimaging device 2 is higher than that of the known structure since thesize of the optical sensors 4 is large. In addition, the amount ofcharge which can be carried by the optical sensors 4 increases, and thedynamic range of the solid-state imaging device 2 also increasesaccordingly.

Furthermore, since the thin silicon layer 20 is composed ofsingle-crystal silicon, the mobility of electrons and holes issufficient, unlike that in polycrystal silicon and amorphous silicon.Therefore, the problem of afterimage or the like does not occur.

In addition, according to the present embodiment, light which enters andpasses through the optical sensors 4 is reflected by the surfaces of thefirst and the second transfer electrodes 12 and 14 or the surface of theinsulating film 30, returns to the optical sensors 4, and is convertedinto electric charge by the optical sensors 4. Even if the returninglight passes through the optical sensors 4 again, it is reflected by thetop surface or the bottom surface of the antireflection film 32, and isconverted into electric charge by the optical sensors 4. Thus, accordingto the present embodiment, multiple reflection of light occurs betweenthe antireflection film 32 and one of the first and the second transferelectrodes 12 and 14 and the insulating film 30. Therefore, the totaldistance which light travels in the optical sensors 4 increases, and thephotoelectric conversion of incident light is extremely efficient. As aresult, sufficient sensitivity can be obtained even when the size,especially the thickness, of the optical sensors 4 is reduced, and thusthe size of the solid-state imaging device 2 can be reduced.

Furthermore, when the material and the thickness of the insulating film30 are suitably selected such that light reflected by the surface of theinsulating film 30 and light reflected by the surfaces of the transferelectrodes interfere with each other so as to intensify each other, theintensity of the reflected light further increases and the sensitivitycan be increased accordingly. Similarly, when the material and thethickness of the antireflection film 32′ are suitably selected such thatlight reflected by the top surface of the antireflection film 32 andlight reflected by the bottom surface of the antireflection film 32interfere with each other so as to intensify each other, the sensitivitycan be further increased.

In addition, since the absorption coefficient of silicon for visiblelight reduces as the wavelength increases (toward the red region), thedepth of the optical sensors 4 is in the range of several micrometers toabout 10 micrometers in order to maintain the sensitivity at the red andnear-infrared regions in the known structure. However, according to thepresent embodiment, the depth of the optical sensors 4 is not limited.In addition, when the optical design is adequately performed under theconsideration of the refractive index and the thickness of theinsulating film 30 and the antireflection film 32 and the wavelength oflight, a solid-state imaging device having high sensitivity for anywavelength can be obtained.

In the present embodiment, the signal charge is read out by theinterlace method. However, the structure in which each of the opticalsensors 4 is provided with three transfer electrodes and the signalcharge is simultaneously read out from all of the optical sensors 4 canalso be easily obtained.

Next, a second embodiment of the present invention will be describedbelow.

FIG. 3 is a sectional side view of a part of a solid-state imagingdevice according to the second embodiment of the present invention, andFIG. 4 is a plan view showing a part of the solid-state imaging deviceaccording to the second embodiment. FIG. 3 is a sectional view of FIG. 4cut along line C-C′. In the figures, components similar to those shownin FIG. 1 are denoted by the same reference numerals, and explanationsthereof are thus omitted.

With reference to the figures, a solid-state imaging device 44 accordingto the second embodiment is similar to the known IT-IS solid-stateimaging device with respect to optical sensors 4 and the structure fortransferring the signal charge. However, it is different from the knownsolid-state imaging device or the solid-state imaging device 2 accordingto the above embodiment in that electrodes according to the presentinvention function as overflow drain electrodes.

The solid-state imaging device 44 has a semiconductor substrate 46 whichis constructed by laminating a support substrate 16, a buffer layer 18,and a thin silicon layer 20, and overflow drain electrodes 48(electrodes according to the present invention) are embedded between thebuffer layer 18 and the optical sensors 4, that is, between the bufferlayer 18 and the thin silicon layer 20. As shown in FIG. 4, one overflowdrain electrode 48 is provided for each column of the optical sensors 4such that it extends along the columns of the optical sensors 4.

In addition, n+ regions 58 are formed in a surface region of the thinsilicon layer 20 which is in contact with the overflow drain electrodes48.

Each of the optical sensors 4 is provided with first and second surfacetransfer electrodes 50 and 52, the first and the second surface transferelectrodes 50 and 52 being formed on the thin silicon layer 20 on theside opposite to the buffer layer 18. As shown in FIG. 4, the first andthe second surface transfer electrodes 50 and 52 are alternatelyarranged along the columns of the optical sensors 4. In addition, thefirst and the second surface transfer electrodes 50 and 52 are providedin common for the optical sensors 4 on each row, and therefore, theyextend along the rows of the optical sensors 4. As shown in FIG. 3,n-type regions 54 are formed in the thin silicon layer 20 at positionsunder the first and the second surface transfer electrodes 50 and 52 ascharge transfer paths. In addition, p+ regions 56 are formed between anoverflow barrier 26A and n-type regions 54, and n− regions 60 are formedbetween the charge transfer paths and the optical sensors 4. As shown inFIG. 3, the first and the second surface transfer electrodes 50 and 52are covered with a light-shielding film 62.

In the solid-state imaging device 44 constructed as above, unnecessarycharge accumulated in the optical sensors 4 can be removed by applying apositive voltage to the overflow drain electrodes 48.

Although one overflow drain electrode 48 is provided for each column ofthe optical sensors 4, the structure may also be, of course, such thatone overflow drain electrode 48 is provided for each row of the opticalsensors 4 or for each of the optical sensors 4.

Pixel reduction, electronic zooming, highly-functional electronicshutter, etc., can be achieved using the overflow drain electrodes 48.

More specifically, in the solid-state imaging device 44, when a positivevoltage is applied to the overflow drain electrodes 48 on alternatecolumns and the signal charge accumulated in the corresponding opticalsensors 4 is removed, alternate columns of pixels can be eliminated andan image whose width is reduced to half can be obtained. In the knownstructure, the speed at which the signal charge is read out is increasedby eliminating alternate rows of pixels in order to achieve a finderfunction in which monitor images are displayed at a high frame rate orto perform automatic focusing and automatic exposure with highperformance. However, since the pixels can only be eliminated in unitsof rows, the aspect ratio of the obtained image is different from thatof the original image. In comparison, if the alternate columns of pixelsare eliminated using the overflow drain electrode 48 as above inaddition to eliminating the alternate rows of pixels, the aspect ratioof the original image can be maintained. In addition, since the numberof pixels is reduced to one-fourth, the frame rate can be furtherincreased.

If one overflow drain electrode is provided for each of the opticalsensors 4, the structure may also be such that, for example, the signalcharge generated by the optical sensors 4 in the peripheral region iseliminated and only the signal charge generated by the optical sensors 4in a central, rectangular region is read out. When electronic zooming isperformed, only the signal charge generated by the optical sensors 4positioned in a certain region is used. Accordingly, when the abovefunction is used in electronic zooming, the signal charge which isgenerated by the optical sensors 4 positioned in a certain region (forexample, the optical sensors 4 in a central, rectangular region) can beselectively read out. Therefore, the image can be obtained in a shorttime. In addition, in the case in which moving images are displayed,they can be displayed at a high frame rate.

In addition, the dynamic range can be increased by using the overflowdrain electrodes 48 as an electronic shutter and setting thecharge-storage time of the optical sensors 4 corresponding to theadjacent pixels to different values. More specifically, the storage timeis set to a long time (which means that a positive voltage is applied tothe corresponding overflow drain electrode 48 at an early time) for oneof the two adjacent pixels, and is set to a short time (which means thata positive voltage is applied to the corresponding overflow drainelectrodes 48 at a late time) for the other pixel. In such a case, if alarge amount of light enters, charge saturation occurs at pixels with along storage time but does not occur at pixels with a short storagetime, and the light can be detected at the pixels with a short storagetime. Therefore, when the amount of light is large, the image signal maybe generated using detection results obtained at the pixels with a shortstorage time. On the contrary, when the amount of light is extremelysmall, the detection results obtained by the pixels with a long storagetime may be used so that the image can be captured with sufficientsensitivity even if the light is weak.

In addition, the dynamic range can also be increased by the followingmethod. That is, first, an image is captured while a certain storagetime is set for all of the optical sensors. Then, map data showing theamount of incident light at each pixel is created. Then, regions wherecharge saturation has occurred are determined on the basis of the mapdata. The storage time for the optical sensors 4 positioned in regionswhere charge saturation has not occurred is unchanged, and the storagetime for the optical sensors 4 positioned in regions where chargesaturation has occurred is reduced. Accordingly, when the image iscaptured again, charge saturation does not occur in any region and ahigh-quality image can be obtained.

In addition, also in the solid-state imaging device 44, multiplereflection of light occurs between the antireflection film 32 and theoverflow drain electrodes 48 and the total distance which light travelsin the optical sensors 4 increases. Accordingly, the light detectionsensitivity is higher than that of the known structure.

Next, an embodiment of a method for manufacturing a solid-state imagingdevice according to the present invention will be described below.

FIGS. 5A, 5B, and 5C are process diagrams of an example of a method formanufacturing a solid-state imaging device according to the presentinvention, and FIGS. 6A, 6B, and 6C are process diagrams showingprocesses performed after the process shown in FIG. 5C. Each of thefigures shows a sectional side view of a part of a substrate structurein the corresponding process among the processes for manufacturing thesolid-state imaging device. In the figures, components similar to thoseshown in FIGS. 1 and 2 are denoted by the same reference numerals.

In the present embodiment, a method for manufacturing theabove-described solid-state imaging device 2 will be described as anexample. First, as shown in FIG. 5A, trenches 68 for separating opticalsensors from one another are formed at constant intervals in a firstsurface 66 of a silicon substrate 64 composed of single-crystal silicon.

Next, as shown in FIG. 5B, device-separating regions 8 are formed byfilling the trenches 68 with a device-separating material. The materialfor filling the trenches 68 may be silicon oxide or silicon nitride sothat it functions as a stopper in a chemical mechanical polishing (CMP)process, which is performed afterwards, and blocks light. Then,channel-stop regions (not shown) are formed by selectively implantingp-type impurity ions at high concentration such that the channel-stopregions extend perpendicular to the trenches 68 with gaps providedtherebetween in the direction perpendicular to the page. Then, p−regions 26 having low-concentration p-type impurities are formed byimplanting ions through the first surface 66 of the silicon substrate 64at low energy.

Next, an insulating film (not shown in FIGS. 5A to 5C and FIGS. 6A to6C), which corresponds to the insulating film 30 shown in FIG. 1, isformed on the first surface 66 of the silicon substrate 64, and firstand second transfer electrodes 12 and 14 (only the first transferelectrode 12 is shown in FIG. 5B) are formed for each row of the opticalsensors such that they extend along the rows of the optical sensors 4.

Then, as shown in FIG. 5C, a buffer layer 18 is formed by depositing,for example, silicon dioxide onto the first and the second transferelectrodes 12 and 14.

Then, as shown in FIG. 6A, a support substrate 16 composed of, forexample, silicon, is bonded on the buffer layer 18. Then, the entirebody is placed such that a second surface 72 of the silicon substrate 64faces upward, and the silicon substrate 64 is polished by the CMPprocess until bottom end portions (top end portions in FIG. 6A) of thedevice-separating regions 8 appear in the second surface 72.Accordingly, the thickness of the silicon substrate 64 is reduced and athin silicon layer 20 is obtained. In this process, the bottom endportions of the device-separating regions 8 are used as CMP stoppers.

Next, as shown in FIG. 6B, the optical sensors 4 are formed in thesilicon substrate 64 by implanting impurity ions through the secondsurface 72 of the polished silicon substrate 64.

Next, an antireflection film (not shown in FIGS. 6A to 6C) is formed onthe surfaces of the optical sensors 4. Then, as shown in FIG. 6C, alight-shielding film 34 having apertures at positions corresponding tothe optical sensors 4 is formed on the second surface 72 of the siliconsubstrate 64 with an insulating layer provided therebetween. Then, aplanarizing film 38 composed of an insulating material, a color filter40, and an on-chip lens 42 are successively formed. According to theabove-described processes, the solid-state imaging device 2 which haselectrodes behind the optical sensors 4 and which provides theabove-described effects is manufactured.

In the method for manufacturing the solid-state imaging device 2according to the present embodiment, the p− regions 26, which functionas an overflow barrier, are formed by implanting ions into the siliconsubstrate 64 through the first surface 66 thereof at low energy beforethe electrodes are formed on the first surface 66 of the siliconsubstrate 64, the overflow barrier being positioned under the opticalsensors 4 when the solid-state imaging device 2 is completed.Accordingly, it is not necessary to implant the ions deep into thesilicon substrate at high energy from the front of the solid-stateimaging device 2 to form the overflow barrier as in the known structure.Therefore, the profile of the implanted impurities can be reliablycontrolled and the thickness of the overflow barrier can be reduced.

As a result, a distance which light reflected by the first and thesecond transfer electrodes 12 and 14 toward the optical sensors 4travels in the overflow barrier, which does not contribute tophotoelectric conversion, can be reduced compared to the distance whichthe reflected light travels in the optical sensors 4. Therefore, thereflected light is effectively converted into electric charge by theoptical sensors 4, and the optical detection sensitivity increases.Accordingly, the size of the optical sensors 4 can be reduced and thenumber of pixels in the solid-state imaging device 2 can be increasedaccordingly.

In addition, in the method for manufacturing the solid-state imagingdevice 2 according to the present embodiment, the overflow barrier isformed by implanting ions into a surface region, and it is not necessaryto perform ion implantation at high energy. Since the ion implantationcan be performed at low energy, the solid-state imaging device 2 can beeasily manufactured.

In addition, in the manufacturing method according to the presentembodiment, the bottom end portions of the device-separating regions 8are used as CMP stoppers when the silicon substrate 64 is polished toreduce the thickness thereof. Therefore, the thickness of the polishedsilicon substrate 64 (the thin silicon layer 20) can be accuratelycontrolled.

The solid-state imaging device 44 according to the above-describedsecond embodiment may also be manufactured by a method similar to theabove-described method for manufacturing the solid-state imaging devicewith regard to the structure in which the electrodes are provided behindthe optical sensors. In this case, one electrode may be provided foreach column of the optical sensors 4, or for each of the optical sensors4.

INDUSTRIAL APPLICABILITY

In the solid-state imaging device according to the present invention andthe solid-state imaging device manufactured by the method according tothe present invention, the electrodes are disposed between the bufferlayer and the optical sensors, that is, behind the optical sensors.Accordingly, when, for example, the electrodes are used as chargetransfer electrodes, it is not necessary to arrange the charge transferelectrodes on the light-receiving surfaces of the optical sensors. Inaddition, when the electrodes are used as overflow drain electrodes,unnecessary charge stored in the optical sensors can be removed byapplying a voltage to the electrodes.

1. A solid-state imaging device having a plurality of optical sensorswhich are adjacent to one another, comprising: a buffer layer comprisingan insulating material; a single-crystal silicon thin film provided overthe buffer layer; the plurality of optical sensors provided in thesingle-crystal silicon thin film and arranged in a matrix pattern suchthat the optical sensors are adjacent to one another; and electrodeswhich are disposed between at least portions of the buffer layer and thesingle crystal having the optical sensors and which control transfer ofsignals generated by the optical sensors, the signals being generatedwhen the optical sensors receive light; a barrier overflow regionlocated directly beneath each optical sensor and extending at leastsubstantially across a region of the entire corresponding opticalsensor; and a transfer path region located directly beneath the barrieroverflow region.
 2. A solid-state imaging device according to claim 1,further comprising an insulating film interposed between the electrodesand the optical sensors.
 3. A solid-state imaging device according toclaim 2, wherein the insulating film reflects light incident from theoptical sensors up toward the optical sensors.
 4. A solid-state imagingdevice according to claim 1, wherein the electrodes reflect lightincident from the optical sensors up toward the optical sensors.
 5. Asolid-state imaging device according to claim 3, further comprising anantireflection film which is provided above the optical sensors andwhich prevents reflection of light incident on the optical sensors.
 6. Asolid-state imaging device according to claim 1, wherein each of theoptical sensors has more than one of the electrodes, and the signalcharge generated by the optical sensors on each column is transferred bythe corresponding electrodes along the column of the optical sensors. 7.A solid-state imaging device according to claim 1, wherein the signalcharge generated by the optical sensors is removed by the electrodes. 8.A solid-state imaging device according to claim 1, wherein the overflowbarrier is disposed under the optical sensors but above the transferpath, and is formed in the single-crystal silicon thin film materialwithin which the optical sensors are formed.
 9. A solid-state imagingdevice according to claim 1, wherein the overflow barrier is formed byimpurities implanted into the single-crystal silicon thin film, theoverflow barrier being positioned under the optical sensors.
 10. Asolid-state imaging device according to claim 1, wherein the overflowbarrier disposed under the optical sensors is formed in thesingle-crystal silicon thin film material within which the opticalsensors are formed, the transfer path region also being formed in thesingle-crystal silicon thin film material, and wherein both the overflowbarrier and the transfer path regions are at least substantiallycoextensive with boundaries of a corresponding optical sensor.
 11. Asolid-state imaging device having a plurality of optical sensors whichare adjacent to one another, comprising: a single-crystal silicon thinfilm; the plurality of optical sensors provided in the single-crystalsilicon thin film and arranged in a matrix pattern such that the opticalsensors are adjacent to one another; and a barrier overflow regionlocated between each optical sensor and a transfer path region beneaththe barrier overflow region located in single-crystal silicon thin filmand wherein both the overflow barrier and the transfer path regions areat least substantially coextensive with boundaries of a correspondingoptical sensor.
 12. A solid-state imaging device having a plurality ofoptical sensors which are adjacent to one another, comprising: a bufferlayer comprising an insulating material; a single-crystal silicon thinfilm provided over the buffer layer; the plurality of optical sensorsprovided in the single-crystal silicon thin film and arranged in amatrix pattern such that the optical sensors are adjacent to oneanother; and electrodes which are disposed between at least portions ofthe buffer layer and the optical sensors and which control signal chargegenerated by the optical sensors, the signal charge being generated whenthe optical sensors receive light, and wherein all portions of atransfer path region are separated from the optical sensor by theoverflow barrier region.